Capacitive pressure sensors are known in the art. These sensors comprise at least one flexible diaphragm having a metalized portion thereon forming one electrode of a pressure sensing capacitor that is movable with respect to a second electrode. It is often the case that the second electrode comprises another metalized portion on a second flexible diaphragm. The capacitance of the sensor is directly related to the dielectric constant of the material in the gap separating the two or more capacitive plates. Undesirable or unaccounted for changes in the dielectric constant of the material within the capacitance gap effects the accuracy and the repeatability of the capacitance measurements. Capacitance sensing units often separate flexible diaphragms from other parts of the sensor by a spacer which serves to seal the volume therebetween therein isolating this volume from the changeable characteristics of the media whose pressure is being sensed. To obtain a dielectric constant that is relatively stable, in the presence of changeable pressure and temperature conditions, the prior art has filled the capacitance gap with a material such as silicon oil. Silicon oil is chosen because its viscosity is nearly constant over a wide temperature range, however, when precise measurements are required, silicon oil is not totally satisfactory. In addition, those pressure sensors which utilize a fluid as a dielectric material display a sluggishness in their measurement characteristics arising from the mass of fluid which must be moved. In addition, other transient measurement errors will be introduced when the sensor is placed in an accelerating environment. These transient measurement errors are amplified when the pressure sensor is used in a hostile aircraft environment which is subjected to high levels of rotational and longitudinal acceleration as well as high levels of aircraft vibration.
It is an object of the present invention to accurately measure pressure. An advantage of the present invention is that the differential pressure transducer produces a capacitive signal reflective of the pressures to be measured and that this signal is immune from undesirable changes in the dielectric constant of the pressure media. In addition, the electrodes and dielectric gap of the capacitor are isolated from the pressure media. Contaminatative and corrosive actions on the electrodes and electrical effects of conductive particle precipitates are thereby avoided.
The present invention relates to a differential pressure sensor comprising a chamber that is adapted to communicate with a first and second source of pressure to be measured. The sensor comprises a central support member circumferentially supported about the chamber for dividing the chamber into smaller first and second pressure receiving chaambers so that the first and second chambers communicate with the first and second pressure sources. The central support member comprises a substantially flat member having peripheral dimensions comporting with the interior dimensions of the chamber and further having a hole therein. The sensor further includes a first flexible diaphragm having a pressure responsive region thereon. The first diaphragm is preferably coaxially oriented relative to the center of the central support member. The first diaphragm is mounted in a parallel spaced apart alignment relative to a first side of the central support member. The sensor further includes a second flexible diaphragm oriented and mounted to the other side of the support member. The first and second diaphragms are mounted to the central support member by a peripheral glass frit seal to hermetically seal the diaphragms to the central support member. The pressure sensor further includes a spacer such as a post received through the hole in the central support member to join the interior, opposing surfaces of the two flexible diaphragms. In this manner, the deflections of both diaphragms are dependant and proportional to the pressure differential thereacross. In addition, the pressure transducer contains a plurality of electrodes deposited to the central support member and to the diaphragms for establishing the electrodes and ground shield of a pressure responsive capacitor. In one embodiment, the transducer utilizes two substantially annular coaxially situated electrodes deposited to the central support member about the hole. The central support member further includes a pair of radial leads partially extending from the location of the peripheral glass seal to the edge of the support member. Each flexible diaphragm comprises a disc having smaller dimensions than the central support member and further including an annular electrode have radially extending leads. During manufacture, the radial extending leads of the diaphragms are oriented in vertical alignment relative to the partial extending leads located on the central support member. Since the partial radially extending leads extend beyond the corresponding leads located on the underside of the flexible diaphragms, the electrical connection to the electrodes located on the undersides of the diaphragm is conveniently accessible through the partial leads.
Many other objects, purposes and advantages of the invention will be clear from the detailed description of the drawings.